1. Field of the Invention
The present invention relates to transmission/reception of data between information processing apparatuses, and transmission/reception of image data photographed by an image pickup apparatus.
2. Description of the Related Art
An image photographed by an image pickup apparatus is usually utilized by being transferred to and stored in a computer. This is because a flash memory card mainly used as a storage medium of an image pickup apparatus is more expensive in the cost per storage capacity than a storage medium (a hard disk, an MO (magnetooptical) disk or the like) of a computer. Accordingly, an image pickup apparatus is usually utilized in the sequence of “a photographing operation→transfer of image data to a computer→storage of the transferred data in a storage medium of the computer”.
The size of image data is relatively large from among the sizes of data dealt with in a computer, and is increasing year by year in accordance with an increase in the number of pixels of an image photographed by an image pickup apparatus. Accordingly, a certain amount of waiting time is produced when the user intends to transfer images to a computer at a time after returning from photographing operations.
A filing system is constructed on a storage medium mounted in an image pickup apparatus, so that images are recorded in the form of files. Similarly, a computer records images in the form of files. That is, transfer of image data from the image pickup apparatus to the computer can be considered as transfer of files.
Conventionally, when a waiting time is produced in file transfer (including in this case copying of files), a display indicating the degree of progress is performed. That is, the degree of completion in the entire transfer processing is indicated, for example, by a percentage, during the waiting time. The user can thereby know an approximate remaining time until completion of transfer (end of the waiting time). Such a display will be hereinafter termed a “transfer-progress display”.
The transfer-progress display is performed according to the following two approaches.                (1) Transfer-progress display based of the number of a file.        (2) Transfer-progress display based of the size of files (=the size of transferred data).        
The two approaches are realized in the following manners.                (1) Transfer-progress display based of the number of a file        
This display is used, for example, when assigning a plurality of (a large amount of) files on a window for displaying files on the picture surface of a computer, and copying a file to another folder. The total number of files to be transferred is first checked before the start of transfer, and the transfer-progress display is updated every time a file is copied.                (2) Transfer-progress display based of the size of files        
This display is used, for example, when downloading a file in an Internet browser. The size of a file to be transferred is first acquired before the start of transfer, and the transfer-progress display is updated whenever necessary during the transfer, based on the size of received data.
A transfer-progress display during image transfer from an image pickup apparatus to a computer will now be considered. In any of the above-described approaches (1) and (2), if a large amount of images to be transferred are present, a delay from the start of transfer processing to a transfer-progress display is produced, because of the following reasons.                (1) In the case of a transfer-progress display based of the number of a file        
For example, problems arise when selecting a command such as “transfer all images” in software of image transfer from an image pickup apparatus, which operates in a computer. In this case, the software in the computer does not know the number of images within the image pickup apparatus. In order to acquire the number, the software requests the image pickup apparatus to transmit a summary of image files. The image pickup apparatus counts the number of images to be transmitted, in response to this request. The computer knows the number of images within the image pickup apparatus only after receiving a response to the request, and assumes a state in which a transfer-progress display can be performed. However, since, for example, the image pickup apparatus has a processing speed lower than the processing speed of the computer, a flash memory has an access speed lower than the access speed of an ordinary DRAM (dynamic random access memory), and there is a limitation in the transfer speed between the image pickup apparatus and the computer, a certain amount of time is required from provision of the request until reception of a response if a large amount of image files are present.                (2) In the case of a transfer-progress display based of the size of files        
Software of image transfer from an image pickup apparatus, which operates in a computer must know the total size of data to be transferred (file sizes), when intending to perform a transfer-progress display according to this approach. For that purpose, it is necessary to provide the image pickup apparatus with a request to transmit file sizes for all images to be transmitted. Upon reception of the request, the image pickup apparatus calculates the total amount of data of image files to be transmitted from a filing system, and transmits a response to the computer. Accordingly, when a large amount of files to be transmitted are present, a considerable amount of time is required for acquiring the size of all data to be transferred (=the sum of file sizes of all images to be transferred).
The object of the transfer-progress display is to display a progress of image transfer whenever necessary during image transfer because a considerable time is required for transferring the entire images. Accordingly, the transfer-progress display becomes meaningless if a considerable time is required from the start of processing until the transfer-progress display appears.